Heimdal plugin define UseKrbCompat if BUILD_KRBCOMPAT
Heimdal plugin define UseKrbCompat if BUILD_KRBCOMPAT

When building the Heimdal plugin if BUILD_KRBCOMPAT rules are
being used define UseKrbCompat as a wix variable so that the
appropriate merge modules can be included.

Change-Id: I3e0b3a4a0b7db657618734e181ab61af9fc924e1

secure-endpoints/netidmgr,secure-endpoints/netidmgr,secure-endpoints/netidmgr,secure-endpoints/netidmgr,secure-endpoints/netidmgr